When looking through a window pane the perceived visual impression is influenced by the window pane through which the light rays pass in order to reach the eyes of the viewer. In addition, the window pane itself may be used as a medium on which information may be displayed to the viewer.
Document DE 20 2008 004 715 U1 discloses an arrangement for illuminating the edge of a vehicle side window, wherein the illumination system is fixedly attached to the lower edge of the side window pane and emits light into the window pane. According to the document, the window pane is easy to locate even in darkness. It is in particular possible to detect the upper edge of a frameless window, e.g. in a cabriolet. It also reduces the risk of leaving the vehicle with open windows when it is dark outside.
In a nautical environment it is known to use red and green discs in order to determine the color of a navigation mark. By looking through the discs one at the time, it may be distinguished if the color is red or green at a longer distance as compared to if only using the naked eye.